The answer to this is simple, it's called home country bias/tax advantages etc. In the US, eagles would we prefered to foreign coins. In the UK, there's usually a slight premium on sovereigns and Britannias. In Germany its kaiserreichs and France its gold francs etc. This home country bias is more prevalent amogst the lay person and new stackers due to recognisability, familiarity, harking back to a more simpler, glorified past in our respective countries (Napoleon etc) and also the tax advantages. You are obviously more experienced and know bullion silver is silver. But coins/rounds are not pure bullion.
For eagles, there was a surge in domestic demand causing large premiums, this has bled into premiums for eagles on the international market, but to a lesser extent. It's also a nice coin as already mentioned. These will come down as demand for ASE's abates, the secondary market regurgitates, and they will be available for a dime a dozen (above manufactured spot) as they were in 2018.
I'm not sure if the same principle applies to kooks and maples, as their mints have been spamming the international markets at various times. Smaller countries will also be more open to foreign coins generally. Here in the UK we are a more refined bunch, with good premiums for both domestic and foreign coins 😉